Arm and tension link hoist for dump bodies



Sept. 23, 1952 u J, M GWlNN, JR 2,611,642

ARM AND TENSION LINK HOIS';1 FOR DUMP BODIES Filed 0G11. 13, 1949 v 2 SHEETS-SHEET 2 Patented Sept. 23, 1952 'ARM AND TENSON LINK HOISTFR DUMP BODIES f' Joseph M. Gwinn, Jr., Dearborn, Mich., assigner to Gar Wood Industries, Inc., Wayne, Mich., a

corporation of Michigan Application October 13, 1949, Serial No.V 121,106

(C1. zas-zz) Claims.

This invention relates to hydraulically operated arm and link hoist mechanismsfor raising the body of a dump truck to dumping position.

It is the principal object of the invention to provide an arm-type hoist mechanism which is more efficient than comparable systems heretofore known, thereby permitting the use either of operating cylinders of'smaller diameter or lowerV operating pressures in the hydraulic system.

This object is accomplished by means of a hydraulically actuated linkage mechanism in which the moment arm of the hoisting force varies with the degree of body lift in about the same manner as the moment arm of the load.v Thus, it is high, and in excess of those heretofore employed in comparable arm-type hoist mechanisms at` the beginning of lift, and gradually decreases to low value, or zero, when the desired dumping angle is reached. It will be appreciated that by virtue of this characteristic the actual force delivered by the hydraulic cylinder is less` at the beginning of the lift than heretofore, and, furthermore, is in proportion tothe load Vand therefore relatively constant throughout the entire angle of body pivot. In terms of the hydraulic equipment which energizes the lifting force, this means that at the option of the designer the hydraulic cylinder may be reduced in diameter, thereby permitting a reduction in the weight of the unit and the body mounting height, or the hydraulic pressure` reduced, thus reducing theV cost and wear. In terms of the linkage structure, the lower and relatively constant lifting force means less highly stressed and more leillciently used elements.

The present design is such that it also has other desirable features. Among these are a high dumping angle and a low height in collapsed condition, the latter feature enabling the body and the center of gravity of the truck to beL lowered.

Briefly, according to the invention, the hoist mechanism is arranged so that the link which connects the arm to the body and applies the lifting force to the body is stressed in tension so that A preferred embodiment of theA invention is shown by way of illustration in the accompanying drawings in which:

Figure 1 is a perspective view of the improved hoist mechanism;

Fig. 2 is a side elevation of the-improved mechanism;

Fig. 3 is a diagrammatic view of the linkage in lowered, intermediate, and dumping positions; and

Fig. 4 is a diagram showing how the lever arms of load and the lifting forces and the oil pressure vary with the angle of tilt of the body.

The invention is shown applied to a dump truck chassis I having a separately manufactured subframe 3 aiiixed thereto, the latter having journals 5 for pivotally receiving the trunnions 1 of the body 9 to establish a hinge connection therewith. The invention is preferably assembled as a part of the sub-frame, but, obviously, may be connected directly to the chassis.

The improved hoist mechanism includes a pair A oflaterally spaced arms I3 that are fixedly interwardly from the axis of the arms I3 and at its upper end has a pivotal connection 2l with a it pulls the body upwardly. In comparable prior `being impossible with prior comparable designs wherein the pressure approached zero with an increase in the angle of lift.

tting 23 that is rigidly affixed to the end of a piston rod 25 that extends rearwardly from the pressure cylinder 21. The latter has a pivotal connection v29 with the sub-frame 3 and it will be noted that this connection is offset beneath the axis of the cylinder 2'I and that the pivotal connection 2I of the rod to the web I5 is offset above the axis of the cylinder. This double oii'set provides increased leverage and other advantages described and claimed in a copending application Serial No. 164,761, filed May 27, 1950, entitled Offset Cylinder and Piston Rod Mounting for Hydraulic Dump Bodies of the present inventor. However, it will be understood that the present 'invention may be employed with pressure cylinders that are mounted in the conventional manner.

In the lowered position of the body 9 that is shown in Fig. 2, the arms I3 extend forwardly and upwardly from their xed pivot connection II-I 9 so that the upper ends thereof and of the web I5, as well as the upper side of the cylinder 2l, are just beneath the underside of the body. The upper end of each of the arms I3 is connected to the body 9 by means of a pair of tension links 3i that are pivoted thereto at 33. The links 3i extend downwardly and preferably also rearwardly so as to achieve maximum collapse (minimum height) of thelinkage in combination with ahigh dumping angle and most efficient operation. Pins 35 connect together the lower ends of the links and pivotally connect them to and between pairs of attachment plates 37 that are rigidly afiixed to the underside of the body 9 .and-extend downwardly therefrom, the plates 3l being spaced so that they and stop plates 4i, vto be described hereinafter, fit within the side members ofthe subfra-me 3.

When it is desired to raise the body 9, the pressure cylinder 21 is energizedby conventional means to force the rod 25 rearwardly. This pivots the web I 5 and arms 23 rearwardly and also the arm-link pivots 33; There is a tendency for the pivots 33 to move away from-the linkbody pivots 35 but this is'prevented since these pivots are interconnected 'by the links 3l. The latter are therefore placed 'in tension and apply a lifting force in tension to the `body -9 through the medium of attachment' plates 31. Thebody is thus pulled upwardl f instead of pushed,as heretofore. L,

Stops to provide positive'limits'to movement of the links 3| relative to the attachment plates 3l during upward movement-are provided. These may comprise plates 4I that are located on the pins 35 and welded to the Y'outsideof the plates 31. They haverigid inwardly extending Vlugs 43, the upper faces' of which abut the longitudinal sides of the links inthe upper position, as shown in Fig. l. As indicated in Fig. 3,`the links 3l in the present embodiment describe an arc of approximately 180f` about Vthe pivots 33 and relative to the sub-framed, andin practicalf ly all modifications this are will at leastl 'exceed 90 unless very low dumping angles aredesired.

Fig. 4 shows the manner `in whichthe moment arms relative to pivot `5`1 of the' load and body 9 and Yof the lifting force applied by links '3i arm of the cylinder force '(the-line of actionof which passes through pivots 23 zand lvabout armpivot l1, (2) the lever arm of link Si about pivot i7, and (3) :the lever arm of link 3i about body hinge 5 7.' Nevertheless, with the present design, the eective moment v.arm ofthe lifting force, which is equalto (ll) (3)./ (2) follows the pattern of the 'load `moment arm with the exception of the brief divergence during the first few degrees of tilt, as shown-.in Fig. 4. This latter is due to the inclination of link si and if it is desired to eliminate it, the link 3i should be vertical in the fully lowered position.

Lifting ofthe body 9 involves, of course, -essentially a balance between `the moment of the liftingV force and the moment of the load about pivot kaxis 5-'l. In the present design, the relationship between the moment arms of these two forces is relatively constant or at least they vary in the same direction, i. e., rapidly decrease with increase of angle of tilt. Since the moment arms are in relatively constant proportion, the forces involved are too. Thus, the force which the piston rod 25 must supply is relatively constant. Consequently, as evident .from Fig. 4, the oil pressure in the cylinder 2l is relatively constant and the peak pressure is ,only a little greater than the mean pressure.

It is, therefore, not necessary as in the past to yineiiiciently design the cylinder 2l and the linkage to withstand momentary high pressures and forces that vare necessary to overcome a lack of moment arm. On the contrary, in this design, since Vthe loads on the pressure-actuated means and linkage are relatively constant, they may be designed to operate at substantially full and most eiicent capacity through the entire angle of tilt. Y

The low vertical height of the present hoist mechanism has already been mentioned, and it :should alsobe noted that the present design also permits .high dumping angles and control by design of the oil pressures involved. One of the limiting factors in prior arm-type hoist mechanisms has been that the lifting force dead centered on the arm pivot, such as would (but does not) occur if the line of force in link 3l passed through pivot 1?-13. Ifthis happened, the moment of the resistance to movement applied by the link 3i to the arm i3 would be zero and so, therefore, would be the oil pressure. Thus, in prior art hoists whereinA the'link dead centers first on rthe arm hinge, it is seen that inherently the oilpressure approaches Zero as the body elevates to movethe link toward dead center 'on the arm pivot'. However, the mean oil pressure is independent of hoist design and a function of the work done in elevating the load. Herma-since the meanV oil 4pres-- sure kis unchangeable, the lowjoil pressures obtained at `one angle of tilt had, in the prior art designs, to be balanced by high oilepressures at another angle resulting in higher maximum yoil pressures than necessary with the -hoist of vthis invention.

In thepresent design, however, the mechanical advantage is progressively decreasing and the link approaches closer to deadA center on the body hinge 5 7 than to dead center on the arm pivot l'i-IS. This is shown in Fig. 3. If the link Si were to pass dead center'on hinge 5-', before the'line of force of the gravity load reached dead centerron the hinge 5--l, the lifting force would become ineffective and the moment of resistance applied to arm I3 infinite and so, therefore, would the oil pressure infoylinder 21. Thus, it is seen that the inherentftendency in the present design is'for-'the oil pressure and link loads to approach'innity. fThis, of course, is easily avoided by so proportioning the linkage that the center of gravity of the load reaches dead center on the body hinge before the line of link 3l passes through the body hinge. In addition, the previously described lugs i3 positively prevent the'link '3i from pivoting relative to the body far enough to assume the dotted line dead center position illustrated "in Fig. 3.

Control of the geometry of the design enables V.the 'designer to control the oil pressure at elevated ous pivot points, including .the body hinge-5 1,

depend to a large extent upon the angle through which the center of gravity of the load must Swing between its lowest position and the position in which it is located directly above the body ii. In a ldump truck, the combination of a body i having a fixed pivotal axis, a rigid member exunless the load dead center angle is less than 63 so that the load will dead center on the body hinge before the link 3i dead centers on the body hinge. For any load dead center angle larger or smaller than 63 the optimum proportions may be determined by out and try. All factors considered, optimum results with the present linkage are obtained when the linkage is proportioned to obtain an oil pressure curve similar to that of Fig. 4 which is calculated for an eight ton batch load under worst conditions, i. e., that part of the load behind the hinge 5-1 is dumped at about a 50 angle. The actual oil pressure curve is parallel but displaced upwardly from the curve of Fig. 3, due probably, to the effects of friction. It will be noted that the oil pressure is a maximum at the beginning of lift and at a point near the end of the lift, both values being approximately equal. To achieve that result which, of course, is related to the shape of the moment arm curve, the link 2| is inclined slightly when the body is in its lowest position, vas shown in the drawings. Y

It will be observed that the angle of tilt before the link 3| dead centers on the body hinge increases as the length of the link 3l and as the angle of its forward inclination approaches zero (i. e., the horizontal) and decreases as the distance between the body hinge 5 7 and the arm hinge r11-i9 increases. However, it is usually desirable to make the distance between the arms and body hinges a maximum so as to obtain the benefits of the increased mechanical advantage. It should be noted that the line of .force in link 3i should not intersect the line of centers of the body and arm hinges when the body is in lowered position or the link will dead center on the arm hinge in the early stages of lifting and, furthermore, jamming diiculties may be encountered.

Those in the art will recognize otherbenets and modifications of the invention, hence it is not intended to limit it to the foregoing description.

What is claimed is:

i. In a dump truck, the combination of a body having a pivotal axis, a rigid member extending downwardly from the body, an arm having a pivotal axis, when the body is in lowered position said arm extending from its pivotal axis toward the free end of the body and alongside the member but above the lower part of the member, a link pivoted at its upper end to the arm at a portion alongside the member and at its lower end to the lower part of the member, and means for applying a lifting force to the arm to pivot it upwardly and toward the body pivot about its own pivot whereby the link is stressed in tension.

tending downwardly from the body,'an arm having a xed pivotal axis spaced forwardly of the body axis when the body is in lowered position, said arm extending forwardly and upwardly from its pivotal axis and'alongside the member but above the lower end of the member, a downwardly and rearwardly extending link pivoted at its upper end to the arm at a position alongside the member and at its lower end to theA lower end of the member, means for applying a lifting force to the arm to pivot it upwardly and rearwardly about its fixed pivot whereby the link is stressed in tension and is pivoted upwardly and rearwardly upon the arm as the arm is pivoted, said link being arranged to first approach a dead center position on the body pivot rather than on the fixed arm pivot. v

5. In a dump truck, the combination of a body having a fixed pivotal axis, two laterally spaced pairs of rigid attachment plates extending downwardly from the underside of the body and adapted to i'it within the side frame members of the truck chassis or sub-frame, said plates in each pair having inwardly extending lugs the upper faces of which form limit stops, a pair of laterally spaced arms including a rigid cross piece lhaving a fixed pivotal axis forward of the body pivot axis, when the body is in lowered position said arms extending forwardly and upwardly be- .tween said plates, downwardly and' rearwardly extending pairs of links between each pair of plates and pivoted at their upper ends to the arms and at their lower ends to the plates. and pressure-actuated means connected to the cross piece for pivoting the arms upwardly and rearwardly about their iixed axis whereby tensile lifting forces are applied to the links and thus to the plates and body, during upward movement of the body said links describing an arc ofapproximately one hundred eighty degrees with respect to their lowermost position before abutting against said stops and said links being arranged to first approach dead center positions on the fixed body pivot rather than on the fixed arm pivot.

JOSEPH M. GWINN, Jn.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,947,328 Burrows Feb. 13. 1934 2,232,230 Gruber Feb. 18, 1941 2,314,531 Wachter Mar. 23, 1943 

